/**
 * Copyright (c) 2021 Darius Rückert
 * Licensed under the MIT License.
 * See LICENSE file for more information.
 */

#include "saiga/core/util/perlinnoise.h"

#include "internal/noGraphicsAPI.h"

#include <algorithm>
#include <cmath>
#include <numeric>
#include <random>

namespace Saiga
{
// THIS IS A DIRECT TRANSLATION TO C++11 FROM THE REFERENCE
// JAVA IMPLEMENTATION OF THE IMPROVED PERLIN FUNCTION (see http://mrl.nyu.edu/~perlin/noise/)
// THE ORIGINAL JAVA IMPLEMENTATION IS COPYRIGHT 2002 KEN PERLIN
// I ADDED AN EXTRA METHOD THAT GENERATES A NEW PERMUTATION VECTOR (THIS IS NOT PRESENT IN THE ORIGINAL IMPLEMENTATION)
// Initialize with the reference values for the permutation vector
PerlinNoise::PerlinNoise()
{
    // Initialize the permutation vector with the reference values
    p = {151, 160, 137, 91,  90,  15,  131, 13,  201, 95,  96,  53,  194, 233, 7,   225, 140, 36,  103, 30,  69,  142,
         8,   99,  37,  240, 21,  10,  23,  190, 6,   148, 247, 120, 234, 75,  0,   26,  197, 62,  94,  252, 219, 203,
         117, 35,  11,  32,  57,  177, 33,  88,  237, 149, 56,  87,  174, 20,  125, 136, 171, 168, 68,  175, 74,  165,
         71,  134, 139, 48,  27,  166, 77,  146, 158, 231, 83,  111, 229, 122, 60,  211, 133, 230, 220, 105, 92,  41,
         55,  46,  245, 40,  244, 102, 143, 54,  65,  25,  63,  161, 1,   216, 80,  73,  209, 76,  132, 187, 208, 89,
         18,  169, 200, 196, 135, 130, 116, 188, 159, 86,  164, 100, 109, 198, 173, 186, 3,   64,  52,  217, 226, 250,
         124, 123, 5,   202, 38,  147, 118, 126, 255, 82,  85,  212, 207, 206, 59,  227, 47,  16,  58,  17,  182, 189,
         28,  42,  223, 183, 170, 213, 119, 248, 152, 2,   44,  154, 163, 70,  221, 153, 101, 155, 167, 43,  172, 9,
         129, 22,  39,  253, 19,  98,  108, 110, 79,  113, 224, 232, 178, 185, 112, 104, 218, 246, 97,  228, 251, 34,
         242, 193, 238, 210, 144, 12,  191, 179, 162, 241, 81,  51,  145, 235, 249, 14,  239, 107, 49,  192, 214, 31,
         181, 199, 106, 157, 184, 84,  204, 176, 115, 121, 50,  45,  127, 4,   150, 254, 138, 236, 205, 93,  222, 114,
         67,  29,  24,  72,  243, 141, 128, 195, 78,  66,  215, 61,  156, 180};
    // Duplicate the permutation vector
    p.insert(p.end(), p.begin(), p.end());
}
// Generate a new permutation vector based on the value of seed
PerlinNoise::PerlinNoise(unsigned int seed)
{
    p.resize(256);
    // Fill p with values from 0 to 255
    std::iota(p.begin(), p.end(), 0);
    // Initialize a random engine with seed
    std::default_random_engine engine(seed);
    // Suffle using the above random engine
    std::shuffle(p.begin(), p.end(), engine);
    // Duplicate the permutation vector
    p.insert(p.end(), p.begin(), p.end());
}
double PerlinNoise::noise(double x, double y, double z)
{
    // Find the unit cube that contains the point
    int X = (int)floor(x) & 255;
    int Y = (int)floor(y) & 255;
    int Z = (int)floor(z) & 255;
    // Find relative x, y,z of point in cube
    x -= floor(x);
    y -= floor(y);
    z -= floor(z);
    // Compute fade curves for each of x, y, z
    double u = fade(x);
    double v = fade(y);
    double w = fade(z);
    // Hash coordinates of the 8 cube corners
    int A  = p[X] + Y;
    int AA = p[A] + Z;
    int AB = p[A + 1] + Z;
    int B  = p[X + 1] + Y;
    int BA = p[B] + Z;
    int BB = p[B + 1] + Z;
    // Add blended results from 8 corners of cube
    double res = lerp(w,
                      lerp(v, lerp(u, grad(p[AA], x, y, z), grad(p[BA], x - 1, y, z)),
                           lerp(u, grad(p[AB], x, y - 1, z), grad(p[BB], x - 1, y - 1, z))),
                      lerp(v, lerp(u, grad(p[AA + 1], x, y, z - 1), grad(p[BA + 1], x - 1, y, z - 1)),
                           lerp(u, grad(p[AB + 1], x, y - 1, z - 1), grad(p[BB + 1], x - 1, y - 1, z - 1))));
    return (res + 1.0) / 2.0;
}
double PerlinNoise::fade(double t)
{
    return t * t * t * (t * (t * 6 - 15) + 10);
}
double PerlinNoise::lerp(double t, double a, double b)
{
    return a + t * (b - a);
}
double PerlinNoise::grad(int hash, double x, double y, double z)
{
    int h = hash & 15;
    // Convert lower 4 bits of hash inot 12 gradient directions
    double u = h < 8 ? x : y, v = h < 4 ? y : h == 12 || h == 14 ? x : z;
    return ((h & 1) == 0 ? u : -u) + ((h & 2) == 0 ? v : -v);
}

double PerlinNoise::fBm(double x, double y, double z, int octaves, float lacunarity, float gain)
{
    float amplitude = 1.0;
    float frequency = 1.0;
    float sum       = 0.0;
    for (int i = 0; i < octaves; ++i)
    {
        sum += amplitude * noise(x * frequency, y * frequency, z * frequency);
        amplitude *= gain;
        frequency *= lacunarity;
    }
    return sum;
}

}  // namespace Saiga
